Compositions which produce a color change upon exposure to light or heat are of great interest in producing images on a variety of substrates. Optical disks represent a significant percentage of the market for data storage of software as well as of photographic, video, and/or audio data. Typically, optical disks have data patterns embedded thereon that can be read from and/or written to one side of the disk, and a graphic display printed on the other side of the disk.
In order to identify the contents of the optical disk, printed patterns or graphic display information can be provided on the non-data side of the disk. The patterns or graphic display can be both decorative and provide pertinent information about the data content of the disk. In the past, commercial labeling has been routinely accomplished using screen-printing methods. While this method can provide a wide variety of label content, it tends to be cost ineffective for production of less than about 400 disks because of the fixed costs associated with preparing a stencil or combination of stencils and printing the desired pattern or graphic display.
In recent years, the significant increase in the use of optical disks for data storage by consumers has increased the demand to provide customized labels to reflect the content of the optical disk. Most consumer available methods of labeling are limited to either handwritten descriptions or preprinted labels which may be affixed to the disk, but which can also adversely affect the disk performance upon spinning at high speeds.
Recently, a variety of leuco dye-containing compositions have been investigated for use on optical disks and other substrates. Typical leuco dye compositions include a leuco dye along with an activator. However, many of these compositions are insufficiently stable under ambient light conditions for practical use. For this and other reasons, the need still exists for improved leuco dye compositions which have improved stability, image forming, and developing characteristics.